The invention relates to tiltable mixers provided with a refractory lining, in particular large-space pig iron mixers, comprising a cylindrical mixing chamber horizontally arranged and having end walls, which mixing chamber is mounted on the base by means of a fixed bearing and an expansion bearing.
It has been known to support pig iron mixers on the base with two spaced-apart raceways fastened to the jacket of the mixing chamber, one of which raceways is mounted in a fixed bearing and the other in an expansion bearing. The raceways are mounted on rollers, the latter being guided by means of cages that are displaceable between the base and the raceways. In order to reach a synchronous movement of the rollers of the fixed bearing side with those of the expansion bearing side, i.e. in order to prevent slanting or travelling of the pig iron mixer to one side, the cages of the expansion and the fixed bearings have to be connected with each other by transverse connections extending parallel to the longitudinal axis of the vessel. A plurality of X-shaped cross-struts is used for that type of connection. Despite those cross-struts, it is not possible in practice to actually reach a synchronous movement of the rollers of the expansion bearing with those of the fixed bearing because, due to differences in the lubrication, the thermal stresses that occur during charging, and discharging as well as unequal friction conditions, relative movements between the rollers of the fixed and expansion bearing sides cannot be totally excluded. Between the roller cages and the rollers play must always be present, so that slanting of the rollers and thus travelling and slanting of the vessel cannot be prevented, despite the cross struts. Slanting of the vessel and the rollers can lead to self-blockage of the rollers, so that the vessel cannot be moved by means of a tilting drive. Due to the line contact of the rollers with the raceways, a vessel, once slanted cannot slide back into its normal position on its own. It happens in fact that, with roller mounted pig iron mixers, when the vessel becomes greatly slanted during a period of several months, it has to be pressed back into its normal position with big hydraulic presses.
In order to avoid these disadvantages and difficulties and according to one proposal, the expansion bearing and the fixed bearing are designed as slide bearings, with the raceways resting on arcuate slideways formed of a plurality of slide plates. Here, the difficulty arises from having to allow the slide plates to contact the arcuate slideways with a certain pressure, i.e. from adjusting a certain pressure distribution over the length of the slideways. In particular, if the slideways deviate from the ideal form of a circular arc--which practically is often the case due to inaccuracies in the production and deformations during operation of a pig iron mixer--not all slide plates will participate in accommodating the load, i.e. some slide plates are subjected to early wear and other slide plates lying between those slide plates are hardly worn at all. A further difficulty is to be seen in the fact that even with ideal circular-arc shaped slideways, adjustment of the slide plates to the shape of the slideways can be carried out only with difficulty and an excessive amount of time.
For further improving and developing the mounting of pig iron mixers it has been proposed to support the slide plates hydraulically. To realize this proposal, a complex construction is required.
If it is desired to use the above-described bearing constructions for tiltable large-space pig iron mixers, whose mixing chambers have diameters of about 10 to 15 meters, the moments at the tilting axis caused by the frictional forces and counteracting the movement of the mixing chamber will appear to be very big. Even with careful mounting according to the above-described proposals, a high portion of the performance capability of the drive motors will have to be used simply for overcoming the frictional forces of the bearings acting at the circumference of the mixing chamber. An increase in the friction with large-space pig iron mixers also occurs because the production of the roller paths and slideways, which have large diameters, cannot be carried out with the tight tolerances that are necessary for an exact mounting.
This high "friction performance portion" must also be taken into consideration when dimensioning the drives, so that, from a certain mixer size onwards, the whole drive has to be designed for a friction performance portion that is disproportionally high compared to the performance portion due to weight and inertia.
A further disadvantage of the known mixer bearings is to be seen in that the production and checking (e.g. measuring) of the roller paths and slideways arranged at the circumference of the mixing chamber is material, time and money consuming. Moreover, the slideways are directly subjected to the changes in shape caused by the deformations of the mixing chamber during operation, whereby the frictional conditions at the bearings, in particular with mixers having large diameters, will deteriorate.